How to modify the traffic source?

You can modify it easily in the behavior tab of your campaign. Click on the startup page to modify it, then click on a "Add a Referrer" and add the referrer you want.

If you want the traffic to look like it comes from Google with "(not provided)" keyword, fill the form with "https://www.google.com".

If you want the traffic to look like it comes from Google with the keyword "YOURKEYWORD", fill the form with "https://www.google.com/search?q=YOURKEYWORD".

If you want the traffic to look like it comes from a social media, fill the form with "https://SOCIALMEDIA.com".